Measuring device for absolute measurement of displacement

Displacement detector 1 generates bi-phase sine wave signals S1A and S1B with a period of P1 in accordance with a displacement L to be detected. Another displacement detector 2 generates bi-phase sine wave signals S2A and S2B with a period of P2 different from the period P1 in accordance with the displacement L to be detected. Wavelength composing means 3 composes the sine wave signals S1A, S2A and the cosine wave signals S1B, S2B output from the displacement detectors 1 and 2 to generate bi-phase sine wave signals, SxA=S1A·S2B−S1B·S2A and SxB=S1B·S2B+S1A·S2A, with a period of Px equal to the least common multiple between the periods P1 and P2. Then, detecting each phase of a fine resolution signal comprising either of outputs from the displacement detectors 1 and 2 and a coarse resolution signal comprising the output signal from the wavelength composing means 3, and computing the displacement L as an absolute position within said period Px based on the phase information.